Method of determining cardiac indicators

ABSTRACT

Methods for determining indicators of left ventricular diastolic function are disclosed. The indicators may include the left ventricular isovolumetric relaxation time and the negative slope of a left atrial “V” wave.

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/691,561, filed Jun. 17, 2005, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to a method for noninvasive monitoring of one or more cardiac performance parameters, and more particularly to a method for monitoring cardiac performance associated with diastolic dysfimction.

BACKGROUND OF THE INVENTION

Heart failure has previously been thought to be due exclusively to poor contractility of ventricles. More recently it has come to be understood that diastolic dysfunction can be a significant factor in heart failure. Diastolic dysftmction is believed to account for as many as 40% of all cases of congestive heart failure (CHF). One indicator of diastolic dysfunction is the time during which the left ventricular muscle relaxes following a contraction. The portion of the cardiac cycle between the end of left ventricle ejection and the opening of the mitral valve is known as the left ventricle isovolumetric relaxation time (LVIVRT). During this time, the left ventricle chamber size is not changing, as the left ventricle is neither emptying nor filling, but there is a change in pressure as the left ventricle relaxes. Another measure of diastolic dysfunction is the rate of filling of the left ventricle.

Measurement of diastolic dysfunction can be performed using invasive techniques, but there are significant risks to the patient. One such prior art technique uses a pressure sensing catheter inserted into the left ventricle via the pulmonary artery. However, the risks to the patient from using the pulmonary artery catheter preclude routine use. Alternatively, heart chamber function can be measured using echocardiograpy, which is safer than pulmonary catheterization and can be used either transthoracically or by esophageal echocardiography. However, echocardiography is difficult to perform, less accurate, and impractical to use for longer than a few minutes at a time. Consequently, it is difficult to obtain an accurate evaluation of the heart using esophageal echocardiography. Thus, there is a need for a less expensive, faster, and safer (in comparison to ventricular catheterization) method that can be used repetitively in a doctor's office, emergency room, operating room, or hospital setting.

SUMMARY OF THE INVENTION

The present invention provides a method for determining indicators of left ventricular diastolic finction, as well as a method for determining the effectiveness of a cardiac therapy. The indicators of left ventricular function include isovolumetric relaxation time and the negative slope of a V wave obtained from measuring changes in left atrial pressure during diastole.

The method may be performed using an apparatus suitable for measuring indicators of left ventricular function. The apparatus may include a catheter comprising an inflatable balloon for insertion into the esophagus of an individual, a compressor device for pressurizing the balloon, and a means for sensing and recording pressure changes on the balloon. The catheter may be used simultaneously with other medical instrumentation, such as an electrocardiograph (ECG), a blood pressure cuff or other suitable means for measuring blood pressure, and optionally a phonocardiograph, so that contemporaneous measurements of heart beat and atrial pressure changes can be made and recorded.

Additionally, the catheter may comprise a second balloon and a device for sensing and recording changes in aortic pressure. When two balloons are provided, they may be spaced apart so that when one balloon is positioned adjacent to the left atrium, the other balloon is positioned adjacent to the aortic arch. Thus, left atrial and aortic pressure changes on the respective balloons can be measured and analyzed to determine indicators of left ventricle functioning using the method of the invention.

A method according to the invention may comprise the steps of inserting into the esophagus of a person an esophageal catheter having a balloon; positioning the balloon adjacent to the left atrium; pressurizing the balloon and recording changes in balloon pressure over a plurality of heart beats to obtain a left atrial pressure V waveform, while simultaneously recording a plurality of heart sounds corresponding to closure of the aortic valve. From these data, the left ventricular isovolumetric relaxation time may be determined by measuring the time between the occurrence of the heart sound which corresponds to the closure of the aortic valve and the occurrence of the peak of the V waveform. Further, the average negative slope of the V waveform can be determined from the V waveform. It is considered that the negative slope of the V waveform reflects the rate of left ventricular filling. The method may further comprise normalizing of the negative slope of the V waveform to a selected heart beat frequency.

The invention may also include a method for determining the effectiveness of a cardiac therapy in an individual. Such a method may comprise taking an initial measurement of left ventricular isovolumetric relaxation time and/or the negative slope of the left atrial V waveform and subsequently re-measuring one or both of these indicators. If the left ventricular isovolumetric relaxation time is reduced between the initial and subsequent measurements, it is an indicator that the left ventricular function has improved and therefore an effective cardiac therapy has been employed. A steepened negative slope of the V waveform at the subsequent measurement is also an indicator that left ventricular function has been improved and that an effective cardiac therapy has been employed.

The invention may additionally comprise a system for obtaining an indicator of left ventricular finction. The system may comprise an esophageal catheter having at least one balloon, a compressor for pressurizing the balloon, a pressure transducer for measuring changes in pressure of the balloon, a sensor for identifying a time of closure of an aortic valve of the person, a device for measuring the heart rate of the individual, such as a sphygmomanometer, and a computer running software that enables the computer to determine particular events in a heart beat cycle. The sensor may comprise a phonocardiograph machine for identifying heart sounds produced by valve closure. Alternatively, the catheter of the system may comprise a second balloon that is suitable for positioning adjacent to the aortic arch of the person and recording changes in aortic arch pressure to obtain an aortic arch pressure waveform. The aortic arch pressure waveform may comprise a dicrotic notch and the software may enable the computer to determine the time at which the aortic valve closes.

The heart beat events that can be determined by the computer running the software may include the V waveform, time of the occurrence of the peak of the V waveform, the pressure at the time the peak occurs, the time at which the slope of the V waveform changes from negative to non-negative, and the time that the aortic valve of the person closes. By determining these data, the software may enable the computer to determine the left ventricle isovolumetric relaxation time (LVIVRT). The LVIVRT may be determined by measuring the change in time between closure of the aortic valve and the time of the occurrence of the peak of the V waveform. The software may also enable to computer to determine the average slope of that part of the V waveform that immediately follows the peak of the V waveform by determining the change in pressure from the time of occurrence of the peak of the V waveform to the time at which its slope first becomes non-negative, and dividing that pressure change by the change in time between the occurrence of the peak of the V waveform and the time at which the V waveform first becomes non-negative. The software may further enable the computer to normalize the V waveform negative slope value of the individual to a selected frequency of heartbeats, such as one beat per second.

These and other objects, features, and advantages of this invention will become apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings wherein the same reference numerals denote the same or similar parts or items throughout the several views and in which a preferred embodiment of this invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a supine patient associated with an apparatus suitable for use in the present invention.

FIG. 2 is a partial left lateral sectional view of the patient taken along the mid-sagittal plane and showing a partially developed esophageal catheter suitable for use with the present invention.

FIG. 3 is a schematic view of the catheter.

FIG. 4 is a sectional view taken generally along the line 4-4 in FIG. 3.

FIGS. 5 and 6 are sectional views taken generally along the lines 5-5 and 6-6 respectively in FIG. 2.

FIG. 7 is a schematic view of a portion of the catheter in the esophagus and illustrating its relation to the left atrium and aortic arch in a tall male adult to the right of the vertical centerline of the figure, and in a short female adult to the left of the vertical centerline, the illustration of the left atrial/aortic arch relationships along the esophagus being drawn to scale in a direction along the length of the esophagus.

FIG. 8 is a graph of a series of simultaneous waveforms at various esophageal depths of a balloon in a relatively tall subject illustrating changes in the balloon pressure waveform for positioning of the balloon adjacent the left atrium.

FIG. 9 is a graph illustrating a series of consecutive left atrial balloon pressure waves at various balloon inflation volumes and simultaneous ECGs illustrating an improved method of obtaining a quantitative determination of mean left atrial pressure.

FIG. 10 is a graph of a series of simultaneous waveforms of the left atrial and aortic balloons and ECG illustrating the obtaining of systolic time intervals.

FIG. 11 is a graph of a series of simultaneous waveforms of the aortic balloon and ECG illustrating an alternative method of obtaining systolic time intervals.

FIGS. 12 and 13 are each graphs of a series of simultaneous waveforms of the left atrial and aortic balloons and airway pressure illustrating respective alternative ways of obtaining pulse amplitude ratios while performing the Valsalva maneuver.

FIG. 14 is a graph of an idealized left atrial balloon pressure waveform and simultaneous ECG and its relation to various heart waveforms for use in describing the obtaining of an index of cardiac output.

FIGS. 15 and 16 are graphs or tracings, with simultaneous ECGs, of left atrial balloon pressure in a person with leg cuffs restricting blood flow to the legs and with the leg cuffs removed respectively and illustrating the obtaining of an index of cardiac output.

FIG. 17 is a graph or tracing of atrial balloon pressure and the simultaneous differentiated atrial waveform.

FIG. 18 is an illustration of aortic pressure, illustrating an alternative means of obtaining an index of cardiac output.

FIG. 19 is an illustration of aortic pressures taken at the aortic arch and carotid artery respectively, illustrating a means of determining pulse wave velocity.

FIGS. 20 and 21 are graphs or tracings, similar to those of FIGS. 15 and 16, with simultaneous ECGs, of aortic balloon pressure in a person with leg cuffs restricting blood flow to the legs and with the leg cuffs removed respectively and illustrating the obtaining of an alternative or second index of cardiac output.

FIG. 22 is a flow chart of a preferred method of determining mean left atrial pressure.

FIG. 23 is a flow chart of a preferred method of determining systolic time intervals and components thereof.

FIG. 24 is a flow chart of a preferred method of determining pulse amplitude ratios during the Valsalva maneuver.

FIG. 25 is a flow chart of a preferred method of determining an index of cardiac output using the left atrial balloon.

FIG. 26 is a flow chart of a method of determining indicators of left ventricle function.

FIG. 27 is a phonocardiograph sheet presenting waveforms from an electrocardiograph, a left atrial balloon pressure, and phonocardiograph correlated in time.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, the cardiac performance apparatus for noninvasive monitoring, indicated generally at 10, is shown associated with a person P, who may be a patient in a cardiac care setting. The person P is shown in a supine position on a hospital bed, gurney, operating table or the like, which support is indicated at 11. The apparatus includes, as its principal components, a computer including controlling and information processing means 12, such as a computer, and information display apparatus including a monitor 14 and a recorder 16. The controlling and information processing means, which includes a computer, further includes an electrocardiograph (ECG) 18 conventionally having leads 18.1 and 18.2 and a ground lead (not shown), and an automatic sphygmomanometer 21 which is interconnected with a blood pressure cuff 22. The cardiac performance apparatus for non-invasive monitoring additionally includes an esophageal catheter, indicated generally at 20. The automatic sphygmomanometer 21 and blood pressure cuff 22 may be of conventional design and will not be described further. The ECG may also be of conventional design. While other suitable leads, such as limb leads, could be employed with the ECG, in most cases it will only be necessary to use “lead II” (which is the signal produced by negative lead 18.1 and positive lead 18.2 when applied to the patient in the manner shown). Lead II will produce a good visualization of the P waves, which will be used for timing purposes as set forth below. While lead 18.1 is shown connected to the upper right chest, it may be connected to the shoulder, or right arm. Similarly, the positive lead 18.2 is shown associated with the lower left chest, but it may be connected to the upper left abdomen, or to the left lower leg. The trunk positions are the standard positions used for continuous monitoring in hospitals and by paramedics and Emergency Medical Technicians.

Now, with reference to FIGS. 3 and 4, it can be seen that the catheter 20 includes an integral double lumen flexible tube 24 having an outer wall 24 a and an inner wall or partition 24 b. These walls define lumens 26.1 and 26.2, which are separated from each other by the inner wall 24 b so that fluid (typically air) entering one lumen cannot enter the other lumen. The tubing 24 is preferably an extruded biocompatible generally non-elastic plastic such as, for example, Dow Pellethane 3883-80AE material with 20% barium sulfate and 1% titanium dioxide, and has a diameter of perhaps about 0.13 inch (3.3 mm). The thickness of the outer wall 24 a and of the partition 24 b may perhaps be about 0.015 inches. On the distal end portion of the tube are mounted a pair of spaced apart balloons 28.1 and 28.2, respectively. The distal end of the double lumen tube 24 terminates at a closed end, illustrated at 24 d, beyond the distal balloon 28.1, which end is suitably closed and/or sealed such as by heat seal, epoxy, or the like. Closed end 24 d is located perhaps about 1.5 cm beyond the distal balloon 28.1. The upper or proximal end portion of the tube 24 is provided with a suitable coupling 30. The coupling 30 connects the lumens 26.1 and 26.2 to substantially identical fluid lines 32.1 and 32.2, respectively, for flow communication therebetween. Each of the lines 32.1 and 32.2 is interconnected with a pressure compensated microphone (34.1 and 34.2, respectively) and a pressure transducer (36.1 and 36.2, respectively), as discussed hereinafter. Each of the lines is also connected to a source of fluid under substantially constant pressure, such as compressor 38 (FIG. 1) through suitable valves for pressurization of the respective balloon. In order to reduce dead space and eliminate the need for a stepping motor, the compressor 38 outlet is connected to an accumulator 40 and a pressure regulating valve 42. Downstream, each line 32 may be connected via needle valve 44 and a solenoid operated valve 46. The flow through the needle valves may be suitably timed to obtain the desired balloon pressures. The balloons may alternatively be connected to separate pressure sources or to other suitable pressure sources such as described in my aforesaid patents. The fluid conveying apparatus, which includes fluid lines 32, coupling 30, and valves 42, 44, and 46, is referred to as the “MLAP machine,” (wherein MLAP stands for “mean left atrial pressure”) in the flow charts of FIGS. 22 to 25.

The tubing 24 passes through openings in the distal and proximal ends of each of the balloons 28.1 and 28.2, which openings are sealed to the tube in an air tight manner so that each of the balloons can be inflated. The balloons may be composed of polyurethane film or other suitable material which is generally non-elastic yet highly compliant. When inflated, the balloons 28.1 and 28.2 have diameters of perhaps about 8 mm and 11 mm, respectively and have suitable overall lengths as described hereinafter. Since the balloons are deflated during insertion of the catheter and since the catheter is otherwise of small diameter, the catheter may be easily inserted without undue discomfort to the patient. To provide for flow between the balloon and the source of fluid under pressure, inflation openings are provided in the lumen wall portions (in the tube outer wall 24 a) which are within the balloons respectively. Thus, there are perhaps three longitudinally spaced 18 gauge (about 0.033 inch diameter) openings 26.11 extending through the wall portion 24 a of lumen 26.1 which lies within the distal balloon 28.1. Similarly, there are perhaps four longitudinally spaced 18 gauge openings 26.22 extending through the wall portion 24 a of lumen 26.2 which lies within the proximal balloon 28.2. The number and size of such openings may vary. In addition to providing flow means for pressurization of the respective balloons, the openings are provided to facilitate, when the balloons are properly positioned in the esophagus, as discussed below, transmission to the pressure compensated microphones 34.1 and 34.2 of sound waves from the mitral and aortic valves, respectively, for listening thereto and/or obtaining analog or digitized representations thereof.

The pressure transducers 36.1 and 36.2 process pressure waves from the balloons 28.1 and 28.2, respectively, in a manner described in my aforesaid patents. Similarly, microphones 34.1 and 34.2 process sound waves from the balloons 28.1 and 28.2, respectively, in a manner similar to that described in my previous patents. The signals from transducers 36.1 and 36.2, microphones 34.1 and 34.2, ECG leads 18.1 and 18.2, and pressures from blood pressure cuff 22 are suitably processed by the controlling and information processing means 12, which is programmed to suitably process the information to obtain and display the outputs described hereinafter on display apparatus 14 and 16, using principles commonly known to those of ordinary skill in the art to which this invention pertains.

Referring to FIGS. 2, 5, 6, and 7, there is illustrated the placement of the balloons 28.1 and 28.2 within the esophagus ES of a person P for the purpose of noninvasively obtaining and monitoring cardiac performance parameters, as hereinafter discussed. FIG. 5 illustrates the relationship of the esophagus ES to the left atrium LA and right atrium RA of the heart H, ascending aorta AA, lungs L, pulmonary trunk PT, descending aorta DA, and vertebrae V at the position of placement of distal or left atrial balloon 28.1 within the esophagus ES, and illustrates this balloon adjacent the left atrium LA. The mitral valve MV and aortic valve AV of the heart H are illustrated in FIG. 2, which also illustrates the relationship of the left atrium LA to the aortic arch AAR along the length of the esophagus ES. FIG. 6 illustrates the relationship of the esophagus ES to the aortic arch AAR, sternum ST, superior vena cava SV, trachea TR, and vertebra V at the position of placement of proximal or aortic balloon 28.2 within the esophagus ES, and illustrates this balloon 28.2 adjacent the aortic arch AAR.

The catheter 20, which has a suitable length, which is preferably at least about 80 cm.(from the coupling 30 to the distal end), is inserted distal end 24 d first through nasal passage NP, pharynx PH, then into the esophagus ES. If desired, the catheter may alternatively be inserted through the mouth. The tubing 24 desirably has markings (not shown), such as a marking at each centimeter along its length to indicate the distance from the end 24 d so that the balloons can be properly positioned as discussed hereinafter. Although the esophagus ES is illustrated in FIGS. 2 and 7 open over its length for ease of illustration, it is well known to those of ordinary skill in the art that the esophagus is normally collapsed and closes about any objects such as the catheter contained therein. When the catheter is inserted to its proper depth, balloon 28.1 will be positioned underneath (when the subject is in a supine position) and adjacent the left atrium LA of the heart H as shown in FIGS. 2, 5, and 7.

In accordance with the preferred embodiment of the present invention, the balloons 28.1 and 28.2 may be spaced apart on the tubing 24 a distance of, for example, about 4 cm and have lengths (suitable lengths as illustrated in FIG. 3) so that, when lower or distal balloon 28.1 is adjacent the left atrium, illustrated at LA in FIGS. 2, 5, and 7, the upper balloon 28.2 is adjacent the aortic arch, illustrated at AAR in FIGS. 2, 6, and 7, and generally below the aortic arch over a substantial portion thereof, as illustrated in FIG. 2. This will allow pressures adjacent both the left atrium and the aortic arch to be sensed in a manner more fully set forth below. In addition, the sounds of the mitral valve MV and aortic valve AV can be picked up for processing without moving the catheter 20 once it is positioned.

The length of the distal balloon is desirably minimized so as to lie adjacent the left atrium over most of its length for good pressure coupling and so as to reduce any interference by the aorta or otherwise with its reception of the left atrial pressure waves. In accordance with these objectives, the overall length of the balloon 28.1 is selected to be preferably between about 1.5 and 3.5 cm, more preferably about 2.5 cm (with a taper at each end of perhaps about 0.25 cm). The overall length of the balloon 28.2 may suitably be about 3.6 cm (with a taper at each end of perhaps about 0.3 cm).

FIG. 7 illustrates to the left and right sides of the centerline 48 of an esophagus ES, the left atrial/aortic arch spatial relationships for a short female P_(SF) (height of about 5′2″) and for a tall male P_(TM) (height of about 6′1″).

These illustrated relationships are drawn to scale in a direction longitudinally of the esophagus. As illustrated in FIG. 7, the distance to the left atrium centerline 50 of the female P_(SF) is at about 33 cm. along the catheter from the entrance to the nasal passage NP, while the distance to the left atrium centerline 52 in the male P_(TM) is about 40 cm. from the entrance to the nasal passage. Thus, the distance to the left atrium in adults varies widely. However, as seen in FIG. 7, the distance between the left atrium LA and aortic arch AAR is substantially the same in both the tall man and the short woman. Furthermore, it is my belief as a medical doctor that this distance is substantially constant, as illustrated by FIG. 7, in virtually all adults. This substantially constant relationship allows the catheter to advantageously be provided in a single standardized size.

In order to provide a standardized catheter which will suitably fit substantially all adult patients so as to reduce the expense, inconvenience, and complexity inherent in carrying and using a set of catheters of various sizes, in accordance with the present invention, the upper balloon 28.2 may be spaced away from the lower balloon 28.1 the distance set forth above so that when the lower balloon 28.1 is positioned adjacent the left atrium LA, the upper balloon 28.2 is suitably positioned adjacent the aortic arch AAR in either shorter adults, such as P_(SF), or in taller adults, such as P_(TM). It can be seen that with this spacing the upper balloon will not be so near the pulmonary artery PA as to receive interference from the pressure thereof. A greater distance between balloons or a greater length of the upper balloon 28.2 which would place it so high in the esophagus that a gag reflex may be initiated is not considered to be desirable.

My prior patents (U.S. Pat. Nos. 5,048,532; 5,181,517; 5,263,485; 5,398,692; 5,551,439; 5,570,671; and 5,697,375, 6,120,442 and 6,238,349, all of which are incorporated herein by reference, also referred to as “aforesaid patents”) disclose suitable positioning of a balloon beside the left atrium for receiving the pressure waves therefrom for suitably obtaining determinations of mean left atrial and mean left atrial transmural pressures. With the balloon thus suitably positioned, my aforesaid patents disclose suitably obtaining quantitative determinations, from the effects of left atrial pressure on the balloon, of mean left atrial and mean left atrial transmural pressures.

In accordance with the present invention, the balloons 28.1 and 28.2 may be used along with blood pressure cuff 22 and the electrocardiograph, as needed, to noninvasively obtain the pressures and other information needed for suitably monitoring cardiac performance, i.e., systolic time intervals, an index of cardiac output, a measure of pulse wave velocity, left ventricular contractility index (dp/dt/MLAP), and pulse amplitude ratios before, during, and after performing the Valsalva maneuver. After the following discussion of an improvement in the obtaining of a determination of mean left atrial and mean left atrial transmural pressures, the use of the apparatus of the present invention for obtaining determinations of each of the above parameters of cardiac performance will in turn be discussed. The computer may be suitably programmed to implement these procedures, using principles commonly known to those of ordinary skill in the art to which this invention pertains.

Positioning of Catheter

As discussed in my prior patents, the distal balloon 28.1 must be correctly positioned adjacent the left atrium in order to suitably obtain the waveform for determining mean left atrial and mean left atrial transmural pressure. One suitable means of positioning the atrial balloon utilizes a bi-polar electrode (which comprises two spaced electrodes, illustrated at 51 in FIG. 7), which is attached to the catheter 20 just above the balloon 28.1, as disclosed in my U.S. Pat. No. 5,570,671. The bi-polar electrode leads, illustrated at 51 a and 51 b in FIG. 4, are preferably embedded in the material which forms the double lumen catheter in order to prevent their interference with pressure signals. As the electrode 51 is moved up the esophagus, its signals are used to obtain an electrogram at each of a series of incremental depths. The length of the negative portion of the largest absolute value of the P wave is determined for at least one P wave in each incremental electrogram. The depth to the center of the left atrium is selected to be that which corresponds to the incremental electrode depth at which the electrogram therefor shows the greatest negative portion length. The balloon 28.1 is then positioned at that selected depth for obtaining the cardiac performance information as hereinafter discussed.

While the above means for positioning the balloon 28.1 is considered to be very reliable, the bi-polar electrode adds additional cost to the catheter, and there is “wait” time at each increment of position until the electrogram readings “settle down.” In order to eliminate the need for esophageal electrodes, as well as to provide an alternative means for balloon positioning, in accordance with the present invention, the balloon 28.1 may be alternately positioned, if desired, in accordance with the following procedure. With the balloon 28.1 in the stomach (not shown), it is inflated to a suitable pressure of about 6 cm. water pressure. While thus pressurized, the catheter 20, which may be suitably marked at for example 1 cm increments, is drawn up the esophagus starting at a suitable depth of perhaps about 48 cm (from tip of nose to center of balloon 28.1) which is known to be well below the position of the left atrium. Each of the depths is manually inputted to the controlling and information processing means 12.

With reference now to FIG. 8, a five channel graph is illustrated, with segments of the graph being produced at various balloon depths. Thus, the five channel tracing to the left of FIG. 8 shows tracing of balloon pressure at a catheter depth of 44.5 cm. FIG. 8 also shows tracings at depths of 37.5 cm, 36.5 cm, 35.5 cm, 34.0 cm and 33.0 cm.

These tracings are for the tall male PTM. With reference to FIG. 7, it can be seen that at a depth of 44.5 cm, the top of the balloon 28.1 is barely adjacent the bottom of the left atrium LA. However, it can be seen from pressure tracing 202, and more particularly the high gain tracing 204, that the balloon has been pulled up to such an extent that the pressure within the balloon is being influenced by the filling and emptying of the left atrium. This is also shown by the oscillometric waveform 208. All of these tracings are based on signals sent to the controlling and processing means 12 by the transducer 36.1, the means 12 causing these waveforms to be transmitted to the monitor 14 and the recorder 16. The means 12 also receives inputs from the ECG leads 18.1 and 18.2 (lead II), and from the microphone 34.1, (as well as from other inputs), and tracings representative of these signals are shown at 206 and 210, respectively.

While tracings produced by recorder 16 may be used, it is envisioned that most health care professionals will use the monitor 14 to position the catheter. The monitor 14 may, for example, display the balloon pressure 204, depth of distal balloon, oscillometric waveform 208, and simultaneous ECG wave 206 for perhaps the three most recent distal balloon depths so that the balloon pressure waves 204 at these depths may be compared.

As seen in FIG. 8, the tracing 204 of high gain raw balloon pressure shows a modified a, c, v waveform at balloon depths of 44.5 and 37.5 cm. (The balloon pressure waveform is referred to as a modified a, c, v waveform because the “a” peak of the balloon waveform is inverted from the “a” peak of the a, c, v waveform, illustrated at 392 in FIG. 14, of pressures taken from within the left atrium. This waveform is not unusual in some patients. Both troughs and peaks in the waveform, which are points where the slope of the waveform changes between positive and negative and which are indicated in FIGS. 8, 9, and 14 by “a”, “c”, and “v”, are referred to herein as “peaks”. The wave portions which contain these “a”, “c”, and “v” peaks are referred to as “a”, “c”, and “v” waves or waveforms, respectively. FIG. 9 illustrates an externally derived pressure measurement technique which may not work in all persons. The a, c, v waveform extends generally between points 371 and 373 on the idealized atrial balloon pressure curve 370 of FIG. 14.

It has been determined that there is a depth in the esophagus at which there is a major change in the balloon pressure waveform 204 so that the left atrial pressure (a, c, v) waveform is no longer apparent. Moreover, the amplitude of the waveform at this depth has abruptly substantially increased, further indicating that the balloon pressure is being affected by a different pressure source within the body. It is believed that the new waveform, illustrated at 212, at the higher depths (36.5 cm and 35.5 cm in FIG. 8) may be a waveform caused by the pulmonary artery PA. The characteristic left atrial pressure waveform with its much smaller amplitude is no longer apparent at the 36.5 cm depth, indicating that the balloon 28.1 has moved beyond the position of the left atrium. In accordance with the present invention, the balloon 28.1 is thus positioned at a catheter depth slightly below the uppermost depth (36.5 cm in FIG. 8) at which the characteristic left atrial pressure wave (a, c, v) first disappeared. Taking into consideration the size of the left atrium, it is considered preferred that the balloon 28.1 be lowered from this depth (36.5 cm) perhaps about 2 to 3 cm (to a depth of perhaps about 39 cm in this subject) until a good left atrial pressure waveform is seen, and the monitor 14 may be used as an aid in such positioning. The catheter 20 may then be secured to the nose or lip, and the various measures of cardiac performance described hereinafter obtained with the distal balloon 28.1 in position adjacent the left atrium and the proximal balloon 28.2 confidently in position adjacent the aortic arch.

The left atrial pressure signal may be subjected to fast Fourier transform analysis, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains, to correct each frequency component for amplitude and phase shift using a suitable regression equation for the catheter, including a factor for barometric pressure. The true left atrial pressure signal is reconstructed by adding all corrected frequencies, and the correct timing of the waveform reestablished with the ECG.

While positioning of the balloon 28.1 has been described, it should be appreciated that the balloon 28.2, which is maintained in the same spatial relationship to the balloon 28.1, will accordingly be positioned as shown in FIG. 7. Also, while the distances used are for the tall male P_(TM), the same positioning technique would be used for other persons. Thus, as can be seen from FIG. 7, the balloon 28.1 would be moved down for person P_(SF) 2-3 cm after the waveform 212 had been detected.

The aortic balloon 28.2 may alternatively be positioned, after placing it deep in the esophagus and suitably inflating it to, for example, a pressure of 6 cm of water, bringing the balloon 28.2 slowly up the esophagus such as in 1 cm increments and looking for the typical aortic pressure signal, which will be inverted, for reasons discussed hereinafter, using the ECG for timing. Other suitable means may of course be used for positioning the left atrial and/or aortic balloons.

Determining Mean Left Atrial Pressure and Mean Left Atrial Transmural Pressure

My aforesaid patents disclose methods using the oscillometric principle for deteriminig quantitatively mean left atrial and mean left atrial transmural pressures. In accordance with these methods, pressure in a balloon adjacent the left atrium is gradually raised, and the balloon pressure, at peak amplitude of the balloon pressure oscillations (or the peak amplitude of sound waves passing through the inflated balloon) effected by the pressure outside the balloon is noted. In accordance with the oscillometric principle, this balloon pressure is equal to the mean pressure outside the balloon which is acting on it. In other words, when the wall of the left atrium is unloaded such that the mean transmural pressure gradient is zero, the transmission of pressure changes is optimal and is not influenced by compliance of the atrial wall.

It is however believed that the balloon 28.1 may (in some patients) pick up aortic pressure waves (from the descending aorta) which may. combine with the left atrial pressure waves and thus skew the results. It is also believed that this effect is predominant during the period of time between the “c” and “v” atrial wave peaks when rapid changes in aortic pressure are occurring and that this effect is insubstantial during the period of time of the “a” wave portion (which includes wave portions 371 and 372 of the atrial waveform, or between the P wave and the peak of the QRS complex on the ECG, when aortic pressure 390 tends to be relatively constant (as is illustrated in FIG. 14). Therefore, with reference now to the pressure wave of balloon 28.1, as shown at 220 in FIG. 9, in order to more precisely obtain a determination of mean left atrial and mean left atrial transmural pressures, at least in some patients, in accordance with the present invention, the balloon pressure during the “a” wave portion is used (instead of the entire waveform) for determination thereof, as discussed hereinafter.

With the catheter 20 in position, the proximal (aortic) balloon 28.2 is evacuated to perhaps about −20 mm Hg after which perhaps about 0.5 ml of air is added. This balloon 28.2 is connected to the transducer 36.2 to measure esophageal pressure continuously. The distal (atrial) balloon 28.1 is evacuated to perhaps a pressure of about −20 mm Hg then filled at a rate of perhaps about 0.01 ml free air per second.

FIG. 9 shows representative segments A1 to A5 of a series of five graphs or balloon pressure tracings of the actual left atrial pressure waveform 220, amplified by a 10-fold increase in gain and having a simultaneous ECG 300 for timing, in the tall male in a supine position with the balloon pressure steadily increased by adding air in increments of 0.05 ml to the balloon. Thus, the waveform 220 in segments A1 to A5 are with the balloon pressure increased to have balloon volumes of 0.75 ml, 0.80 ml, 0.85 ml, 0.90 ml, and 0.95 ml of air respectively.

Using the ECG 300 for timing, the “a” wave portion, which is part of the entire left atrial pressure wave 220, is identified and the peak to peak voltage, illustrated at 237, of the “a” wave portion 371 or 372 having the highest voltage (highest amplitude) is measured at each of the balloon volumes Al to A5 and stored in computer memory. This peak to peak voltage 237 is a measure of the “a” wave amplitude and represents the maximum voltage difference recorded from the atrial waveform during the time period from the P wave to the peak of the QRS complex on the ECG.

The signals are subjected to fast Fourier transform analysis to correct each frequency component for amplitude and phase shift using a suitable regression equation for the catheter. The true left atrial pressure signal is then reconstructed by adding all corrected frequencies and the correct timing of the waveform re-established with the ECG.

When the left atrial balloon filling cycle is completed, the recordations of the balloon pressure at preferably end-expiration are examined, such as by use of a suitably programmed computer, and the time when one or more, such as 5, contiguous “a” wave portions at a certain balloon volume reached the highest recorded voltages, corresponding to peak oscillation pressure, is identified. The balloon pressures for determining mean left atrial and mean left atrial transmural pressures should be taken at the same point in the respiratory cycle, which is preferably end-expiration. The pressure in atrial balloon 28.1 at that time is identified and displayed on the screen.

Alternatively or additionally, the heart sounds passing through the inflated balloon 28.1 are recorded by pressure compensated microphone 34.1 and suitably digitized, as discussed more fully in my aforesaid U.S. Pat. No. 5,570,671. The mean balloon pressure at preferably end-expiration at the sound wave peak amplitude is suitably inputted to the computer and displayed on the monitor, and the mean left atrial and mean left atrial transmural pressures are determined therefrom and displayed as discussed herein for balloon pressure oscillations.

As discussed in my prior patents,-there is an abrupt slope change from a fast to a slowed rate of pressure increase indicative of the equalization of balloon pressure with the surrounding tissue pressure prior to balloon expansion. This slope change pressure is determined from the atrial balloon pressure-volume curve and inputted to the computer. In order to determine mean left atrial transmural pressure, the pressure (preferably end-expiratory pressure) at this slope change is subtracted from preferably end-expiratory pressure at the balloon oscillation peak, and this pressure may then be displayed by the monitor.

Referring to FIG. 17, there is illustrated at 240 a graph or tracing of pressure in the atrial balloon while adjacent the left atrium and at 242 a simultaneous graph or tracing of balloon pressure oscillations. Tracings 240 and 242 are similar to those of FIGS. 9 and 11 respectively of my aforesaid U.S. Pat. No. 5,263,485, except as hereinafter discussed. The abrupt slope change indicative of the equalization of balloon pressure with the surrounding tissue pressure prior to balloon expansion is shown at 244. The signal for tracing 242 has been differentiated by use of a conventional analog or digital differentiator. As the signal peaks, the rate of voltage change increases, which is displayed by the differentiator. Advantageously, it is not necessary to filter out low frequencies with this technique. As seen in FIG. 17, the differentiated signal allows.one to more clearly see the point of oscillation peak 246 so that mean left atrial and mean left atrial transmural pressures may be more precisely determined.

From the proximal (aortic) balloon 28.2, the esophageal end-expiratory pressure is obtained and inputted to the computer. In order to determine mean left atrial pressure, the esophageal end-expiratory pressure is added to the mean left atrial transmural pressure, and this pressure may also be displayed by the computer.

It was seen in the waveform segments A1 to A5 of FIG. 9 that the peak amplitude 237 of the “a” wave portion 222 occurred at a balloon volume of 0.85 ml (segment A3), which corresponds to a peak oscillation pressure of 16 cm water, which corresponds to a mean left atrial pressure of about 9.5 to 10 mm Hg, which is considered to be a normal value.

The measurement cycle may be repeated at a preset sampling frequency, and the information printed out and used as needed and for the determination of other cardiac performance parameters as discussed hereinafter. A preferred method for determining mean left atrial pressure in accordance with the above discussion is illustrated generally at 650 in the flow chart of FIG. 22.

Determining Systolic Time Interval and Components Thereof

The systolic time interval (QS₂) comprises the duration of time from the beginning of the Q wave on the electrocardiogram to the time of the second heart sound S₂, which is in this case the sound of the aortic valve closing. During this time interval there are the two components or phases of left ventricular systolic activity, i.e., the pre-ejection period (PEP) and the left ventricular ejection time (LVET). PEP refers to the time spent by the ventricle increasing pressure on the volume of blood in it before ejection of the blood into the aorta, and LVET is the duration of the ejection phase. These time interval components may be used in various combinations to gauge ventricular performance. For example, a long PEP indicates that the heart is pumping against increased resistance, and the ratio PEP/LVET is known to decrease as cardiac output increases.

In order to reliably, conveniently, inexpensively, and continuously obtain systolic time intervals and components thereof, in accordance with the present invention, the catheter 20 and the ECG 18 are used preferably in combination, the catheter being provided with a pressure compensated microphone 34.2 with a 100 Hz high pass filter to create an aortic phonocardiograph. Thus, after the catheter is suitably positioned, as hereinbefore discussed, and the aortic balloon 28.2 is suitably inflated to a minimal pressure of perhaps about 2 to 4 mm Hg, the aortic pressure waveform from balloon 28.2, illustrated at 314 in FIG. 10, is suitably recorded and digitized, using the ECG for timing. The phonocardiogram, illustrated at 308, is also suitably recorded. The aortic waveform is desirably analyzed with fast Fourier transform analysis to correct phase shift and frequency components found using suitable equations for the catheter dimensions, and the aortic waveform is then reconstructed by adding the corrected frequency components.

The exemplary aortic pressure signal 314 shown in FIG. 10 was taken with the subject sitting up. When a subject is lying flat, this signal may be inverted due perhaps to the aortic arch moving apart during systole. If the signal is inverted, it should desirably be re-verted electronically to show pressure increases during ventricular ejection.

Referring to FIG. 10, the time of onset Q (302) is obtained from the ECG, illustrated at 300, the QRS complex being shown at 303. The ECG is taken from lead II of the skin ECG. The time of S₂ is taken as the time of beginning, illustrated at 304, of the second heart sound, illustrated at 306, from the aortic phonocardiogram 308. The length of time of the total systolic time interval QS₂ is the time interval between times 304 and 302.

The beginning of LVET is taken as the time of beginning, illustrated at 310, of the upslope, illustrated at 312, of the aortic pressure signal, illustrated at 314, which indicates that the left ventricle has begun discharging blood into the aorta. The aortic pressure signal waveform 314 is taken from the balloon 28.2 adjacent the aortic arch.

The end of LVET is taken as the time, illustrated at 316, of the dicrotic notch, illustrated at 318, of the aortic waveform 314. The difference between times 316 and 310 is the LVET. If the dicrotic notch is badly distorted because of aortic valve pathology, LVET determination may have to be aborted.

PEP is the difference between QS₂ and LVET. However, PEP is still obtainable even if LVET cannot be obtained, as being the difference between times 310 and 302. Thus, while the use of the aortic phonocardiogram is preferred, this is an alternative way of obtaining a determination of PEP whereby at least one and perhaps both phases of the systolic time interval may be determined without the use of a phonocardiogram at all.

If desired for the purpose of determining PEP, the time 310 of beginning of upslope 312 of aortic pressure wave 314 may be suitably corrected for the time delay due to the distance from the aortic valve to the aortic balloon (the correction should be approximated by a constant and short time delay), using principles commonly known to those of ordinary skill in the art to which this invention pertains. However, I believe that the uncorrected time 310 may be normally sufficiently precise for determination of PEP as well as LVET.

FIG. 10 also shows at 319 and 320, respectively, the simultaneous left atrial pressure signal and the unfiltered left atrial phonocardiogram from the distal (atrial) balloon 28.1. The PEP is suitably corrected for heart rate (PEP+0.4 HR), the LVET is suitably corrected for heart rate and sex (LVET+1.7 HR for men, LVET+1.6 HR for women), and the QS₂ is suitably corrected for heart rate and sex (QS₂+2.1 HR for men, QS₂+2.0 HR for women). For beat by beat analysis, these determinations may be averaged for perhaps 10 beats and may be suitably displayed.

Referring to FIG. 11, there is illustrated an alternative procedure for determining LVET. Using the simultaneous ECG 300 for timing, a raw aortic pressure signal (with the proximal balloon 28.2 inflated to a volume of perhaps about 0.7 ml air) is illustrated at 330, and this signal is suitably differentiated to obtain differentiated aortic signal 332. The sharp upslope beginning at point 334, which occurs at the end of the QRS wave, is believed to signal the beginning of LVET. The point 336 is believed to signal the end of LVET because of aortic valve closure (illustrated at AC in FIG. 14) at this point. Thus, LVET, in accordance with this alternative embodiment of the invention, is believed to be the duration of time between points 334 and 336.

A preferred method for determining systolic time intervals and components thereof in accordance with the above discussion is illustrated generally at 660 in the flow chart of FIG. 23.

The ratio PEP/LVET is considered to be a useful index of ventricular performance, with a minimum value indicating optimum performance.

Determination of Pulse Amplitude Ratios During Valsalva Maneuver

The Valsalva maneuver involves having a patient create and maintain an airway pressure with open glottis by blowing into a mouthpiece to pressurize a mercury column to 40 mm Hg. (or, if the patient cannot generate this pressure, perhaps 20 to 25 mm Hg.) and holding it there for 10 seconds. By examining the arterial blood pressure during and immediately after this maneuver, a diagnosis of heart failure may be made since a normal heart and a heart in hypertensive heart failure respond to the maneuver in different ways, as discussed in “Effects of Valsalva's Maneuver on the Normal and Failing Circulation” by E. P. Sharpey-Schafer, British Medical J., Mar. 19, 1955, p. 693 to 695. A healthy heart shows an increase in pulse pressure then damping of the pressure during the Valsalva maneuver, followed by a dramatic increase in pulse pressure and decrease in heart rate with rapid damping of the pulse pressure when the Valsalva maneuver is released. A diseased heart does not respond in this fashion.

In accordance with the present invention, the catheter 20 is used to conveniently and reliably provide a waveform of (1) left atrial pressure by use of the distal (atrial) balloon 28.1 similarly as previously discussed and/or (2) aortic pressure by means of proximal (aortic) balloon 28.2 (while inflated to a pressure of perhaps about 6 mm Hg) as previously discussed. Each of these waveforms will show the characteristics of a normal or failed heart, as the case may be, during and immediately after the Valsalva maneuver is performed.

Instead of being connected to a mercury column, the mouthpiece may instead be connected to a precalibrated transducer and feedback of airway pressure provided to guide the patient. Alternatively, esophageal pressure can be used to demonstrate the Valsalva maneuver without recourse to airway pressure by using the atrial or aortic balloons. The patient should be sitting in an upright position in order for esophageal pressure measurements to be provided by the atrial or aortic balloon, which is evacuated to a pressure of perhaps about −20 mm Hg., then filled with perhaps about 0.4 ml air for this purpose.

FIG. 12 illustrates one method of measuring pulse amplitude ratios following the Valsalva maneuver. Illustrated at 350 is an increase in esophageal pressure (about 30 cm water) as determined by the aortic balloon for a period of time (about 10 seconds) as the Valsalva maneuver is being performed by an upright subject. This is confirmed by simultaneous increased airway pressure (about 40 cm water), illustrated at 352, for the same period of time. Immediately after performance of the Valsalva maneuver, the left atrial balloon waveform, illustrated at 354, shows a dramatic increase in left atrial pressure, and a decrease in heart rate, characteristic of a normal heart. In order that the pulse amplitude pattern of the left atrial balloon pressure may be easy to view and work with, in accordance with the present invention, the left atrial pressure oscillometric waveform 354 is preferably placed on a steady baseline, in accordance with procedures discussed in my aforesaid patents and using principles commonly known to those of ordinary skill in the art to which this invention pertains.

FIG. 13 illustrates an alternative method of measuring pulse amplitude ratios following the Valsalva maneuver. Illustrated at 360 is an increase in esophageal pressure (about 30 cm water) as determined by the left atrial balloon for a period of time (about 10 seconds) as the Valsalva maneuver is being performed by an upright subject. This is confirmed by simultaneous increased airway pressure (about 40 cm water), illustrated at 362, for the same period of time. (Airway pressure is measured by a transducer associated with the mouthpiece.) Immediately after performance of the Valsalva maneuver, the pressure, illustrated at 364, in the proximal or aortic balloon 28.2 shows a pulse amplitude pattern of aortic pressure characteristic of a normal heart. In order that the pulse amplitude pattern of the aortic balloon pressure may be easy to view and work with, the aortic balloon pressure waveform 364 is also preferably placed on a steady baseline. A preferred method for determining pulse amplitude ratios during the Valsalva maneuver in accordance with the above discussion is illustrated generally at 670 in the flow chart of FIG. 24.

Determination of Index of Cardiac Output

In FIG. 14, the pressure in the left atrial balloon 28.1, which has been filled with a gas in accordance with the oscillometric principle set forth above, is illustrated ideally by line 370. FIG. 14 also ideally illustrates, for purposes of relating the timing of various heart events with the atrial balloon pressure line 370, aortic, left atrial, and left ventricle pressures, illustrated at 390, 392, and 394 respectively, and the times of closing MC of mitral valve MV, opening AO of aortic valve AV, closing AC of aortic valve AV, and opening MO of mitral valve MV. The first and second heart sounds are indicated as occurring at times S₁ and S₂ respectively.

In accordance with the present invention, an index of cardiac output is obtained which is based on my belief that the “a” wave portion (caused by left atrial contraction), the “c” wave portion thereof (caused by left ventricular contraction), and the “v” wave portion thereof (caused by pulmonary venous return to the left atrium) of the balloon-sensed left atrial waveform 370 will each increase or decrease in proportion to an increase or decrease in cardiac output, each wave reflecting a different manifestation of cardiac activity. In order to accomplish this, the area under the left atrial balloon pressure curve 370 during a heart beat may be integrated to obtain an index of cardiac output. In order to do so efficiently, the ECG electrodes 18.1 and 18.2 may be connected to the surfaces of the skin of the person P and the catheter 20 is properly positioned with the left atrial balloon 28.1 behind the left atrium (or below if the person P is supine). The left atrial balloon 28.1 is then suitably pressurized, as previously discussed, to peak oscillation pressure (to unload the left atrial wall, the transmural pressure being at this time zero) and is then held at that pressure. As previously discussed, in accordance with the oscillometric principle, when the balloon pressure is at peak oscillation pressure, this balloon pressure is equal to the mean pressure outside the balloon which is acting on it so that the wall of the left atrium is unloaded (the mean transmural pressure gradient is zero). The transmission of left atrial pressure changes is, during this unloaded state, optimal and is not influenced by compliance of the atrial wall. Both the ECG and a phonocardiogram from the left atrial balloon are displayed on the CRT monitor 14 in real time. The health care personnel will evaluate the waveforms being displayed and make a judgement as to whether or not the mitral valve is damaged, which may invalidate the measurements due to back flow of blood from the left atrium.

A preferred method for determining an index of cardiac output using the left atrial balloon pressure waveform in accordance with the above discussion is illustrated generally at 680 in the flow chart of FIG. 25.

Referring to FIGS. 15 and 16, there are shown at 400 and 402 respectively representative tracings of high gain balloon pressure with the balloon in the esophagus adjacent and under the left atrium of a person, and simultaneous ECGs 300. For each of these tracings 400 and 402, an area, illustrated at 401 and 403 respectively (which areas are hatched for ease of illustration) was defined under the respective curve for the length of a single heartbeat, i.e., from the beginning of one QRS complex to the beginning of the next QRS complex, to a base line, illustrated at 405, which corresponds to the lowest pressure during the cycle. Balloon pressure 400 was while leg cuffs restricted blood flow from the legs so that a low cardiac output would be expected. Balloon pressure 402 was taken with the leg cuffs off so that greater cardiac output would be expected. As seen in FIGS. 15 and 16, the area 403 for balloon pressure 402 is greater than area 401 for balloon pressure 400 indicative of greater cardiac output for tracing 402, which is consistent with the leg cuffs being off. By use of impedance cardiography, an increase of 24 percent in cardiac output was measured in the same person (at a different time but under similar conditions) when the leg cuffs were removed, thus confirming the usefullness of the area under an atrial pressure waveform for determining an index of cardiac output.

Referring to FIG. 18, there is illustrated an alternative means of obtaining an index of cardiac output (referred to herein as a second cardiac output index) utilizing the aortic pressure 314 as sensed by the aortic balloon 28.2 adjacent the aortic arch. This is based on the principle that pressure follows volume in the aorta (and elsewhere in the vascular system), i.e., as the stroke volume (the volume of blood flowing in the aorta during each heart beat) increases, the pressure increases, and as stroke volume decreases, the pressure decreases. FIG. 18 shows the aortic balloon pressure curve inverted, i.e., when the balloon pressure is shown to be increasing, it is actually decreasing. Thus, for analysis purposes, the aortic balloon pressure curve 314 is inverted to properly reflect the pressure within the balloon and tissues adjacent the aortic arch. This is because, in theory, the aortic arch AAR, responding to increased flow in the aorta and therefore increased pressure, will open or tend to straighten (the ascending and descending aorta AA and DA respectively move away from each other) like a Bourdon tube. as the pressure rises during systole, and the opening or tendency to straighten the aortic. arch (resulting, with reference to FIG. 6, in the descending aorta DA tending to move away from the aortic balloon 28.2 while the ascending aorta AA remains firmly fixed to the heart) will relieve force acting on the aortic balloon in the esophagus to thus decrease aortic balloon pressure. Similarly, pressure in the aortic balloon will increase when the aortic arch closes as the aortic pressure drops. The observation that the pressure recorded by an esophageal balloon adjacent the aortic arch was inverted with respect to the actual intra-aortic pressure was made by Taquini in 1940. See Taquini, “The Esophageal Pulse Under Normal and Abnormal conditions”, The American Heart Journal, vol. 40 (no. 2), 129-140 (1940).

During systole, the stroke volume is the sum of arterial uptake and systolic runoff or drainage. The arterial uptake is the volume of blood stored in the aorta as a result of distension, this volume being returned to the circulation as diastolic runoff. The arterial uptake acts to increase the aortic blood pressure as previously stated.

Systolic runoff is believed to deflect the aortic arch as a result of Newton's third law of motion acting within the curve of the aortic arch. Thus, blood that is being propelled out and around the aortic arch by the pumping action of the heart exerts a force on the aorta which tends to deflect it. Thus, it is believed that both flow through (systolic runoff) and the arterial uptake may tend to deflect the aortic arch. By inverting the aortic balloon pressure waveforn, the waveform 312 is obtainable which is thus considered to be proportional to aortic deflection. This being so, the area under the inverted pressure/time curve 314 of the aortic balloon pressure wave (for one heart beat) may be determined by suitably filtering the signal digitally and integrating, and this area is believed to be proportional to blood flow or stroke volume, i.e., it indicates greater or lesser flow through the aorta as the inverted balloon pressure curve increases or decreases respectively. Thus, this area is believed to provide an index of cardiac output when multiplied by heart rate.

The full line pressure wave 314 is for a higher pressure/flow. The dotted line pressure wave 502 is illustrated for a lower pressure/flow. In accordance with the present invention, the area under the wave, which thus indicates greater or lesser volume flowing through the aorta, is accordingly integrated and multiplied by the heart rate to determine an index of cardiac output.

Referring to FIGS. 20 and 21, there are shown at 400 and 402 respectively representative tracings, inverted, of aortic balloon pressure with the balloon in the esophagus adjacent the aortic arch AAR of a person, and simultaneous ECGs 300. Tracings thereof, suitably filtered to remove respiratory excursions, are illustrated at 604 and 606 respectively, and the dicrotic notch is illustrated at 608. Illustrated at 610 and 612 are simultaneous tracings of heart sound recordings respectively, illustrating the first and second heart sounds at 614 and 616 respectively. Illustrated at 626 and 628 are tracings of absolute aortic balloon pressures therefor respectively. The period of the heart beat for tracing 604 is shorter than that of tracing 606 because of irregular heart beat due to atrial flutter. For each of these tracings 604 and 606, an area, illustrated at 618 and 620 respectively (which areas are hatched for ease of illustration) was defined under the respective curve for the length of a single heartbeat, i.e., from the beginning, illustrated at 622, of one QRS complex to the beginning 622 of the next QRS complex, to a base line, illustrated at 624, which corresponds to the lowest pressure during the cycle. Balloon pressure 604 was taken while leg cuffs restricted blood flow from the legs so that a low cardiac output would be expected. Balloon pressure 606 was taken with the leg cuffs off so that greater cardiac output would be expected. As seen in FIGS. 20 and 21, the area 618 for balloon pressure 604 per unit elapsed time is less than area 620 for balloon pressure 606 (despite differences in heart rate) indicative of greater cardiac output for tracing 606, which is consistent with the leg cuffs being off. By use of impedance cardiography, an increase of about 25 percent in cardiac output was measured in the same person (at a different time but under similar conditions) when the leg cuffs were removed, thus confirming the usefulness of the area under an inverted aortic pressure waveform for determining an index of cardiac output.

A preferred process for obtaining the second cardiac output index (using the aortic pressure waveform) includes the following steps:

-   a. Connect the skin ECG for timing; -   b. Check for any air leaks in the catheter or MLAP machine; -   c. Insert catheter into the stomach via esophagus; -   d. Position catheter with the distal (left atrial) balloon behind     the left atrium per “MLAP Process.” This automatically positions the     aortic (proximal) balloon; -   e. Deflate the left atrial balloon; -   f. Select the frequency of desired measurement; -   g. Evacuate aortic (proximal) balloon to a pressure of −20 mm Hg; -   h. Gradually fill the aortic balloon with air until a slope change     of the pressure-time curve is encountered, then stop filling; -   i. Add 1.0 ml air to the balloon and close valve. No air is to be     added or removed thereafter until measurement is completed; -   j. Monitor the pressure from the aortic balloon using the     differential transducer and the low-pass filter to remove     fluctuating pressure effects from respirations; -   k. Invert the pressure waveform to make it appear upright and     display on the monitor; -   l. Record the aortic balloon pressure waveforms for several heart     beats (for example, 6) at end of expiration; -   m. Using the ECG for timing, correct the pressure waveform for each     heart beat using fast Fourier analysis; -   n. Calculate the waveform pressure-time integral for each heart beat     relative to a baseline that is defined by the lowest pressure seen     during each heart beat; -   o. Calculate the mean pressure-time integral by summing all 6     pressure-time integrals and dividing by 6; -   p. Calculate the average heart rate that occurred while measuring     the 6 aortic pressure signals using the ECG; -   q. Multiply the mean pressure-time integral by the average heart     rate. This number is an index of cardiac output; -   r. Display the index of cardiac output on the monitor and store it     together with the date and time for future reference; -   s. The computer compares the current index of cardiac output with     prior indices and displays the results on the monitor as “percent     changes in cardiac output”; -   t. At a preselected time interval, return to step f.

Preferably, while the waveforms (left atrial or aortic) are being evaluated on the monitor, or perhaps on chart paper from the recorder 16, the information processing means will collect, for example, six (6) pressure cycles (preferably at end expiration) and corresponding ECGs and will digitize them. The processor 12 is suitably programmed to establish for each waveform a base line corresponding to the lowest pressure observed during the respective heartbeat. The pressure-time integrals are then calculated, summed, and then divided by the number of waveforms to yield a mean value. This mean value is then multiplied by the average heart rate that occurred during the measurements (from analyzing the ECG). This yields an individual index of cardiac output which may then be compared with subsequent or prior indexes to determine whether cardiac output is increasing, decreasing, or remaining constant.

If it is determined that the mitral valve is damaged, the resulting back-flow may invalidate the use of the left atrial pressure wave for obtaining an index of cardiac output, it is preferred in this circumstance to obtain an index of cardiac output using the aortic balloon and aortic pressure waveform (which would not be affected by such back-flow).

The above procedures for obtaining an index of cardiac output may work well for people with various heart conditions such as atrial flutter. While preferably an area under an aortic or left atrial waveform may be suitably processed and integrated and multiplied by the heart rate to obtain an index of cardiac output, FIGS. 15 and 16 illustrate that such a precise analysis may not be necessary in all situations since the differences in area may often be merely eye-balled to give health care personnel the information needed to determine whether a patient's cardiac output is increasing or decreasing or staying the same.

Alternatively, slopes of certain segments of the left atrial and aortic pressure waveforms may be measured to provide an index of cardiac output. However, it is believed that the area under an aortic or left atrial pressure wave, being more comprehensive, provides a more reliable index of cardiac output.

Measuring Pulse Wave Velocity

Pulse wave velocity can be used as an index of arterial rigidity. In order to determine pulse wave velocity, in accordance with the present invention, the distance between the aortic arch and an other artery is divided by the time difference between the pulse at the aortic arch and the pulse at the other artery for the same heartbeat. Thus, the pressure waveform from the aorta is compared with the pressure waveform from another artery. Accordingly, an esophageal balloon is positioned next to the aortic arch, and a point on the pressure wave from the balloon, after being suitably corrected by fast Fourier transform analysis, is compared with the corresponding point on the pressure wave from the carotid (or other suitable) artery which may be detected by a plethysmograph or by a low frequency microphone or otherwise suitably detected. The aortic wave may be used to determine the pulse wave velocity by determining the onset of the pulse wave (indicative of opening of the aortic valve) at, for example, the aortic arch and at another suitable artery, for example, the carotid artery, determining the difference in time and distance there between and deriving therefrom the velocity by dividing the distance by the time in accordance with conventional principles. As the artery becomes more rigid, the pulse wave velocity generally increases. Thus, the pulse wave velocity may be used as an index of artery rigidity, and stroke volume capacity may also be inferred therefrom. Referring to FIG. 19, in order to provide means for easily and reliably determining pulse wave velocity which can be used by paramedical personnel with minimal training, in accordance with the present invention, the aortic pressure waveform 314 provided by the aortic balloon 28.2 adjacent the aortic arch may be suitably corrected by fast Fourier analysis, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains. Preferably, the time period between onsets 310 and 510 of the aortic balloon and carotid (or other) artery signals respectively are determined since the wave tends to become distorted (becomes narrower and higher) with increased distance from the aortic arch. Thus, the time period, illustrated at 500, between the corrected time 310 of onset of the aortic balloon signal 314 and the time 510 of onset of the carotid artery signal 514 of the pulse wave as taken by a plethysmograph 504 is suitably calculated, using principles commonly known to those of ordinary skill in the art to which this invention pertains, and the pulse wave velocity, an index of artery rigidity, derived therefrom as previously discussed.

A preferred process for measuring pulse wave velocity includes the following steps:

-   a. Connect a skin ECG for timing; -   b. Check for air leak in the catheter or MLAP machine; -   c. Insert the catheter into stomach via the esophagus; -   d. Position the catheter with the distal (left atrial) balloon     behind the left atrium per the “MLAP Process”, which will     automatically position the proximal (aortic) balloon; -   e. Deflate the left atrial balloon; -   f. Select the frequency of the desired measurement; -   g. Evacuate the aortic (proximal) balloon to a pressure of −20 mm     Hg; -   h. Gradually fill the aortic balloon with air until a slope change     of the pressure-time curve is encountered, then stop filling; -   i. Add 1.0 ml air to the balloon and close valve. No air is to be     added or removed thereafter until the measurement is completed; -   j. Monitor the pressure from the aortic balloon using a differential     transducer and low-pass filter to remove fluctuating pressure     effects from respirations; -   k. Invert the aortic balloon signal to make it appear upright; -   l. Attach a plethysmograph or low frequency (<100 Hz)     phonocardiograph pick-up over peripheral artery (e.g., carotid,     radial, femoral); -   m. Measure the distance from the selected peripheral artery on the     body surface to the aortic arch (which is at the level of the     sternal angle of Louis where the second rib joins the sternum) and     enter this distance into the computer; -   n. Simultaneously record the aortic pulse from the catheter and the     peripheral pulse from the plethysmograph or phonocardiograph; -   o. Using the ECG for timing, perform fast Fourier transform analysis     and reconstruction to correct the aortic pulse signal for phase     shift and amplitude; -   p. Compute the time difference between the corrected aortic pulse     and the peripheral pulse; -   q. Divide the distance between the aortic and peripheral pulses by     the time difference to determine pulse wave velocity; -   r. Display the pulse wave velocity on the monitor and record in     memory; -   s. At a preselected time interval, repeat steps f to r.     Determining Left Ventricular Contractility Index

It is recognized that the contractility index is a sensitive indicator of cardiac performance. The present apparatus may be used to provide such an index by computing (dp/dt/MLAP), dp being the diastolic pressure less the mean left atrial pressure, and dt being PEP. To this end, the patient P is connected to the ECG electrodes as shown in FIG. 1 and to an automatic blood pressure device 22, also as shown in FIG. 1. (While use of an automatic blood pressure device is the preferred manner for determining blood pressure, other ways may be used to determine blood pressure, such as, for example, by arterial pressure transducers.) After the ECG electrodes have been properly connected, the catheter 20 is inserted into the esophagus in accordance with the procedures set forth above to properly position the left atrial balloon 28.1 behind the left atrium. With the foregoing equipment attached to the information processing means 12, the frequency of desired measurements is entered into the processing means 12. The mean left atrial pressure is determined in accordance with the procedure discussed above. The actual pre-ejection time period (PEP) is determined in accordance with the procedure discussed above, this being equal to “dt” in the equation set forth above. From the blood pressure device, diastolic blood pressure is determined, and MLAP is subtracted from diastolic blood pressure to give the “dp” of the equation set forth above. It is now necessary to only solve the equation and to display the result, an approximation of the index of contractility, on the monitor. A preferred process for determining a left ventricular contractility index includes the following steps:

-   a. Insert the left atrial balloon behind the left atrium in     accordance with the MLAP process, as illustrated in FIG. 22. -   b. Attach skin ECG electrodes. -   c. Connect to output of automatic blood pressure device (or arterial     pressure transducer) or manually input diastolic pressure. -   d. Enter the frequency of desired measurements. -   e. Using the MLAP process of FIG. 22, determine the MLAP. -   f. Using the STI process of FIG. 23, determine the actual PEP, which     equals dt. -   g. From the blood pressure device or manual input, retrieve the     diastolic blood pressure. -   h. Subtract MLAP from the diastolic blood pressure, thereby     obtaining dp. -   i. Calculate from the above dp/dt/MLAP. -   j. Display the result on the monitor. -   k. Repeat steps e to j until the desired number of measurements is     reached.     Measuring Indicators of Left Ventricular Function

The present invention provides a method for determining indicators of left ventricular function. One such indicator is left ventricular isovolumetric relaxation time. A second such indicator which may be determined by the method of the invention is the negative slope of a V waveform, wherein the V waveform is a representation of pressure changes in the left atrium. The terms “V wave” and “V waveform” are used interchangeably herein.

The indicators may be correlated with diastolic dysfunction and may also be used to determine the effectiveness of a cardiac therapy. The indicators may be obtained by measuring changes in left atrial pressure using an esophageal catheter comprising a balloon and coordinating the left atrial pressure changes with particular events in one or more heart beat cycles.

Referring to FIG. 26, the method 700 may comprise the steps of inserting 720 into the esophagus of a person an esophageal catheter having a pressure sensing balloon and positioning 740 the balloon adjacent to the left atrium, pressurizing 760 the balloon and measuring 780 changes in balloon pressure over a plurality of heart beats to obtain a left atrial pressure V waveform, each V waveform having a peak corresponding to the opening of a mitral valve. The method may also include measuring 780 a plurality of heart sounds while simultaneously measuring changes in balloon pressure. From these measurements, the time of occurrence of the peaks of the V waveforms may be identified 800 and the left ventricular isovolumetric relaxation time and the negative slope of a V waveform may be calculated 820.

In order to describe various embodiments of the invention, the terms “first heart sound” and “second heart sound” are used herein to refer to sounds produced by closing heart valves and which are capable of being recorded by a phonocardiograph. In particular, the first heart sound is produced by closure of the mitral valve and is also referred to herein as a “mitral valve closure sound.” The term “second heart sound” refers to a sound which is produced by closure of the aortic valve and may also be referred to herein as an “aortic valve closure sound.”

With respect to the V waveform, which may be obtained by measuring changes in left atrial pressure, the peak of the V waveform is understood by those skilled in the art to correspond with opening of the mitral valve. The negative slope of the V waveform reflects the rate of left atrial emptying into the left ventricle and is understood by those skilled in the art to be an indirect measure of ventricular filling, and therefore an indirect measure of the rate of left ventricular relaxation and/or stiffness.

By determining the time the second heart sound occurs and the time that the peak of the left atrial pressure V waveform occurs, the left ventricular isovolumetric relaxation time (LVIVRT) may be determined.

The negative slope of the V waveform may be calculated by dividing the change in left atrial pressure (ΔP) during left atrial emptying into the left ventricle by the change in time (ΔT) over which the left atrium emptying takes place. The time the left atrium begins emptying is the time immediately after the occurrence of the peak V waveform, at which point the slope of the V waveform becomes negative. Thus, a formula which may be used to calculate the negative slope of the V waveform is ΔP/ΔT. It will be recognized by those skilled in the art that analysis of the V waveform to identify its peak and/or negative slope may be performed in a variety of ways, such as by manual inspection of a V waveform trace or by computer analysis of left atrial pressure changes measured by the balloon 28.1 positioned adjacent to the left atrium.

In order to obtain data which may be used in practicing the method of the invention, the first and/or second heart sounds may be recorded by a phonocardiograph. Examples of phonocardiograms are presented in FIG. 20 at 610 and FIG. 21 at 612, and in FIG. 27 at 940. Also depicted are tracings of heart sound recordings and illustrate the first heart sound at 614 and second heart sound at 616. It will be recognized by those skilled in the art that time of the occurrence of the first heart sound and/or the time of the occurrence of the second heart sound may be ascertained by computer analysis of data recorded by a phonocardiograph without human inspection of a phonocardiograph trace. In one embodiment, an electrocardiogram (ECG) of the individual may be recorded while recording atrial pressure changes via the balloon. The ECG may be useful in coordinating the timing of the atrial pressure changes and the occurrence of valve closings which produce the heart sounds.

Measurements of left atrial pressure changes can be performed for varying lengths of time. It is preferable to record the pressure changes for at least 90 seconds. The catheter may be left in place and operating for a period of hours or weeks.

In one embodiment, the balloon 28.1 positioned adjacent to the left atrium may be inflated to mean left atrial peak oscillation pressure. Without intending to be bound by any particular theory, it is considered that inflating the balloon to mean atrial oscillation pressure provides a more accurate recordation of atrial pressure changes than measurement obtained with a balloon having sub-peak inflation.

In another embodiment, the method may be performed using a catheter which includes a second balloon 28.2. The second balloon 28.2 may be spaced on the catheter relative to the first balloon such that when the first balloon is positioned adjacent to the left atrium the second balloon 28.2 may be positioned adjacent to the aortic arch. An example of such a catheter configuration is depicted in FIG. 2, wherein the first balloon 28.1 and the second balloon 28.2 are shown placed in the esophagus ES. The mitral valve MV and aortic valve AV of the heart H are also shown to illustrate the relationship of the left atrium LA to the aortic arch AAR along the length of the esophagus ES.

The second balloon 28.2 may be used to record changes in pressure in the aortic arch AA. Accordingly, it will be recognized that an aortic arch pressure waveform recorded by the second balloon may include recordation of a dicrotic notch. The time of occurrence of the dicrotic notch may be used as an additional or alternative marker of the time of occurrence of the second heart sound. In this regard, referring to FIGS. 20 and 21, there are shown at 400 and 402, respectively, representative tracings of recorded aortic balloon pressure changes with the balloon in the esophagus adjacent the aortic arch of a person. A simultaneous ECG 300 is also shown. The dicrotic notch is illustrated at 608 of FIG. 20 and in FIG. 27 at DN. Recognition of the dicrotic notch is well within the purview of those skilled in the art. The dicroctic notch may be determined by inspection of a trace from an aortic balloon or by computer program.

FIG. 27 is a representative data sheet obtained from a normal individual. The left atrial pressure recordation trace 900 includes “a” waveforms produced by the atrial contraction, “c” waveforms caused by left ventricular contraction, and “v” waveforms caused by pulmonary venous return to the left atrium, resulting in a rise in left atrial pressure, wherein the “v”s are pointing to the peak of the V waveforms. The portion of the V waveform having a negative slope is the descending portion of the pressure trace 900 immediately following peak v (i.e., to the immediate right of peak v). Also depicted in FIG. 27 is an ECG 920 representing electrical impulse fluctuations in the heart during heart beat cycles, including a second heart sound, as well as a phonocardiogram 940 identifying the occurrence of heart sounds, such as a dicrotic notch DN which occurs simultaneously with the second heart sound on the ECG 940.

The time between the second heart sound and the peak v corresponds to the left ventricular isovolumetric relaxation time. Normal values for LVIVRT are 72±12 milliseconds (ms) for person less than 30 years of age; 80±12 ms for persons 30-50 years of age, and 84±12 ms for persons greater than 50 years of age (Hamlin et al., Am. J. of Crit. Care, 2004, Vol. 13, pages 453-466). Therefore, a shorter LVIVRT may indicate a better functioning left ventricle as compared to a longer LVIVRT, and LVIVRT ranges outside of these normal ranges may indicate that the person has diastolic dysfunction. Also, because the negative slope of left atrial V waveform is considered to be a measure of the rate of left ventricle filling, and therefore a measure of the rate of left ventricle relaxation and/or stiffness, a steeper slope may indicate a better functioning ventricle.

The method may further comprise normalizing of the negative slope of the V waveform of the individual. Normalizing of the negative slope of the V waveform can be performed by using the formula (ΔP/ΔT)/MfH, wherein MfH is the heart beat frequency of the individual. In one embodiment, the negative slope of the V waveform can be normalized to a selected frequency, such as one beat per second. For example, normalizing of the negative slope of the V waveform can be performed by using the formula (ΔP/ΔT)(SfH)/(MfH), where MfH is the measured heart rate in the person being subjected to the method of the invention, and where SfH is a the selected heart beat frequency conversion factor. It is preferred to use one cycle per second as the selected heart rate SfH. For example, if MfH=120 beats per minute, an SfH of 60 beats per minute would yield an (SfH)/(MfH) of 0.5. Normalizing may be useful for comparing negative V waveform slopes obtained from different individuals, or from the same individual over periods wherein the heart rate of the individual varies substantially, such as during a conventional stress test or in response to surgical or pharmacological interventions.

The method of the invention may also be used to determine the effectiveness of a cardiac therapy in an individual by taking an initial measurement of the left ventricular isovolumetric relaxation time and/or making an initial measurement of the negative slope of the left atrial V waveform before or during a cardiac therapy, and subsequently re-measuring one or both of these indicators. A reduced left ventricular isovolumetric relaxation time at the subsequent time may indicate improved left ventricular function and therefore that an effective cardiac therapy has been employed. A steepened negative slope of the V waveform at the second time point may also indicate improved left ventricular function and therefore that an effective cardiac therapy has been employed. Examples of cardiac therapy, the effectiveness of which the present method is suitable for determining include surgical therapies and pharmacological therapies.

System for Measuring Indicators of Left Ventricular Function

Referring to FIGS. 1-3, the invention may be embodied as a system for obtaining an indicator of left ventricular function and, generally speaking, carrying out one or more of the methods described herein. The system may include an esophageal catheter 20 having a balloon 28.1, a compressor 38 for pressurizing the balloon 28.1, a pressure transducer 36.1 for measuring changes in pressure of the balloon 28.1, a phonocardiograph 308 for identifying a time of closure of the aortic valve AV of the person P, a device for measuring the heart rate of the individual, such as a sphygmomanometer 21 or an ECG 18, and a computer 12 running software that enables the computer 12 to determine particular events in a heart beat cycle.

The catheter 20 may include a second balloon 28.2 that is suitable for positioning adjacent to the aortic arch AAR of the person P and recording changes in aortic arch AAR pressure to obtain an aortic arch AAR pressure waveform. The aortic arch AAR pressure waveform may comprise a dicrotic notch. The software may enable the computer 12 to determine the dicrotic notch and thereby determine the time at which the aortic valve AV closes. System may also include a phonocardiograph 34.2 for recording heart sounds.

Heart beat events that may be determined by the computer 12 running the software may include identifying the V waveform, the time of the occurrence of the peak of the V waveform, as well as the pressure at the time the peak occurs, the time at which the slope of the V waveform following the peak becomes non-negative, and the time that the aortic valve AV of the person P closes. From these data, the software may enable the computer 12 to determine the left ventricle isovolumetric relaxation time (LVIVRT) by measuring the change in time between closure of the aortic valve AV and the time of the occurrence of the peak of the V waveform. The software may also enable to computer 12 to determine the average negative slope of part or all of the V waveform following the peak by determining the change in pressure from the time of occurrence of the peak of the V waveform following the peak to the time at which its slope first becomes non-negative, and dividing that pressure change by the change in time between the occurrence of the peak of the V waveform and the time at which it first becomes non-negative. The software may further enable to computer 12 to normalize the V waveform negative slope value by, for example, dividing the negative slope value by the measured heart rate of the person P. If the measured heart rate does not have the desired units, a conversion factor SfH may be used. For example the conversion factor may be used to change the value of the measured heart rate (MfH) from seconds per beat to beats per minute.

Other Cardiac Performance Determinations As discussed above, the catheter 20 and its associated pressurizing and monitoring equipment, along with a standard ECG 18 and blood pressure cuff 22 may be used to inexpensively yet reliably, conveniently, and noninvasively obtain various cardiac performance parameters. The apparatus described herein may also include a phonocardiograph 34.2 for use in obtaining systolic time intervals, as previously discussed, and an automatic blood pressure cuff for continuously monitoring systolic and diastolic blood pressures, which are useful in that the systolic pressure shows the peak pressure that the ventricle can generate while the diastolic pressure is the minimum pressure which the heart has to overcome to cause blood to flow. In addition to a phonocardiograph for the aortic balloon, a phonocardiograph is also provided for the atrial balloon so that the finction of the mitral and aortic heart valves may be analyzed with respect to leakage and resistance to flow. Thus, the noninvasive apparatus described herein is provided, without the need for additional pieces of apparatus which may be expensive or invasive, to inexpensively yet reliably and continuously obtain determinations of major cardiac performance parameters as follows: mean left atrial pressure to determine the priming pressure of the left ventricle; heart valve function analysis, which addresses a problem in the practice of anesthesia wherein changes in heart sound or rhythm need to be recognized immediately; electrographic analysis of the heart's beating frequency and rhythm; systolic time intervals including the ratio PEP/LVET; mean left atrial transmural pressure as an index of left atrial filling pressure unbiased by thoracic pressure changes such as may be caused, for example, by a mechanical ventilator; systolic and diastolic blood pressures; the left ventricular contractility index; two alternative indices of cardiac output; pulse wave velocity; the determination of pulse amplitude ratios before, during, and after the Valsalva maneuver; Esophageal pressure (an established estimate of pulmonary pleural pressure), which can be used in conjunction with other pulmonary measurements to determine (a) the elastic properties of the lungs, (b) lung isovolume pressure-flow curves, (c) the work of breathing, and (d) pressure staking or intrinsic positive end expiratory pressure; left ventricular isovolumetric relaxation time; and the negative slope of the atrial V waveform.

The distal and proximal balloons 28.1 and 28.2, and their spatial relation on the catheter 20, as hereinbefore discussed, advantageously allows one standard catheter to fit virtually all adults and advantageously allows this standard catheter to be easily and conveniently positioned just once for reliably obtaining the pressures and sounds in order to determine the various cardiac performance parameters listed above.

Statements of theory are contained herein to aid in understanding of the invention. Although such statements of theory are believed to be correct, applicant does not wish to be bound by them.

While the best mode of this invention known to applicant at this time has been shown in the accompanying drawings and described in the accompanying text, it should be understood that applicant does not intend to be limited to the particular details illustrated in the accompanying drawings and described above. Thus, it is the desire of the inventor of the present invention that it be clearly understood that the embodiments of the invention, while preferred, can be readily changed and altered by one skilled in the art and that these embodiments are not to be limiting or constraining on the form or benefits of the invention. 

1. A method for obtaining an indicator of left ventricular function of a person comprising: a) inserting into the esophagus of the person an esophageal catheter having at least one balloon; b) positioning the balloon adjacent to the left atrium; c) pressurizing the balloon; d) recording balloon pressure over a plurality of heart beats, wherein the recorded balloon pressure corresponds to left atrial pressure changes and the recorded pressure forms V waveforms each having a peak corresponding to opening of the mitral valve; e) identifying the time of occurrence of the peaks of the V waveforms; f) at the same time as performing step d), recording a plurality of aortic valve closure sounds, wherein each of the aortic valve closure sounds corresponds to a closure of the aortic valve; and g) measuring: i) the time between the occurrence of an aortic valve closure sound and the peak of the first V waveform subsequent to the aortic valve closure sound to obtain a left ventricular isovolumetric relaxation time (LVIVRT), wherein the LVIVRT is an indicator of left ventricular finction; and/or ii) the average negative slope of the V waveform to obtain a V waveform negative slope value, wherein the V waveform negative slope value is an indicator of left ventricular function.
 2. The method of claim 1, further comprising normalizing the V waveform negative slope value to a selected frequency of heartbeats to obtain a normalized negative slope number (NNSN), wherein the NSSN is an indicator of left ventricular function.
 3. The method of claim 2, wherein the computer normalizes the V waveform negative slope to the heart be frequency of the individual by using the formula (ΔP/ΔT)(SfH)/(MfH), wherein ΔP is change in pressure between the pressure determined in f) iii) of claim 21 and the pressure determined in f) v) of claim 21, wherein ΔT is the change in time between the time determined in f) ii) of claim 21 and the time determined in f) iv) of claim 21, wherein MfH is a measured heart rate in the person, and wherein SfH is a selected heart beat frequency conversion factor.
 4. The method of claim 2, wherein the selected frequency is one beat per second.
 5. The method of claim 1, wherein in step c), the balloon is pressurized to approximately peak left atrial oscillation pressure.
 6. The method of claim 1, wherein step d) further comprises measuring a plurality of mitral valve closure sounds.
 7. The method of claim 1, wherein the plurality of aortic valve closure sounds are recorded by a phonocardiograph.
 8. The method of claim 1, wherein the plurality of heart beats comprises at least 60 contiguous heart beats.
 9. The method of claim 1, wherein the catheter comprises a second balloon suitable for positioning adjacent to the aortic arch and recording changes in aortic arch pressure to obtain an aortic arch pressure waveform.
 10. The method of claim 9, wherein the aortic arch pressure waveform is used to determine formation of a dicrotic notch and using the dicrotic notch formation to determine closure of the aortic valve.
 11. A method for obtaining an indicator of the effectiveness of a cardiac therapy in a person, the method comprising: a) inserting into the esophagus of the person an esophageal catheter having at least one balloon; b) positioning the balloon adjacent to the left atrium; c) pressurizing the balloon; d) at a first time point, recording balloon pressure over a plurality of heart beats, wherein the recorded balloon pressure corresponds to left atrial pressure changes and the recorded pressure forms a V waveform having peaks corresponding to opening of the mitral valve; e) identifying the time of occurrence of the peaks of the V waveforms; f) at the same time as performing step d), recording a plurality of aortic valve closure sounds, wherein each of the aortic valve closure sounds corresponds to a closure of the aortic valve; and g) measuring: i) the time between the occurrence of an aortic valve closure sound second and the peak of the first V waveform subsequent to the aortic valve closure sound to obtain a left ventricular isovolumetric relaxation time (LVIVRT), wherein the LVIVRT is an indicator of left ventricular function; and/or ii) the average negative slope of the V waveform to obtain a V waveform negative slope value, wherein the V waveform negative slope value is an indicator of left ventricular function; h) performing cardiac therapy; i) repeating steps d), e) and f) at a second time point subsequent to performing cardiac therapy; wherein a decreased LVIVRT determined for the second time point is an indicator of an effective cardiac therapy, and wherein a steeper V waveform negative slope value determined for the second time point is an indicator of an effective cardiac therapy.
 12. The method of claim 11, further comprising normalizing the V waveform negative slope value to a selected frequency of heartbeats to obtain a normalized negative slope number (NNSN), wherein the NSSN is an indicator of left ventricular function.
 13. The method of claim 12, wherein the computer normalizes the V waveform negative slope to the heart be frequency of the individual by using the formula (ΔP/ΔT)(SfH)/(MfH), wherein ΔP is change in pressure between the pressure determined in f) iii) of claim 21 and the pressure determined in f) v) of claim 21, wherein ΔT is the change in time between the time determined in f) ii) of claim 21 and the time determined in f) iv) of claim 21, wherein MfH is a measured heart rate in the person, and wherein SfH is a selected heart beat frequency conversion factor.
 14. The method of claim 11, wherein the selected frequency is one beat per second.
 15. The method of claim 11, wherein in step c), the balloon is pressurized to approximately peak left atrial oscillation pressure.
 16. The method of claim 11, wherein step d) further comprises recording a plurality of mitral valve closure sounds.
 17. The method of claim 11, wherein the plurality of aortic valve closure sounds are recorded by a phonocardiograph.
 18. The method of claim 11, wherein the plurality of heart beats comprises at least 60 contiguous heart beats.
 19. The method of claim 11, wherein the catheter comprises a second balloon suitable for positioning adjacent to the aortic arch and recording changes in aortic arch pressure to obtain an aortic arch pressure waveform.
 20. The method of claim 19, wherein the aortic arch pressure waveform is used to determine a time at which a dicrotic notch and using the dicrotic notch time to determine closure of the aortic valve.
 21. The method of claim 11, wherein the cardiac therapy is a pharmacological therapy.
 22. The method of claim 11, wherein the cardiac therapy is a physical therapy.
 23. A system for obtaining an indicator of left ventricular finction of a person comprising: a) an esophageal catheter having at least one balloon; b) a compressor for pressurizing the balloon; c) a pressure transducer for measuring changes in pressure of the balloon; d) a sensor for identifying a time of closure of an aortic valve of the person; e) a device for measuring the heart rate of the person; and f) a computer having software running thereon, and the software enabling the computer to determine: i) a peak of a V waveform, wherein the V waveform represents pressure changes in a left atrium of the person; ii) time of the occurrence of the peak of the V waveform; iii) pressure at the time determined in ii); iv) time at which a slope of the V waveform occurring after the peak first becomes non-negative, wherein the time at which the slope of the V waveform becomes non-negative designates the time of the end of a V waveform negative slope; v) pressure at the time determined in iv); vi) time of closure of an aortic valve of the person, wherein the closure of the aortic valve precedes the occurrence of the peak of the V waveform; wherein the software further enables the computer to determine: I) a left ventricular isovolumetric relaxation time, which is a change in time between the time determined in f) vi) and the time determined in f) ii); and/or II) an average slope of part of the V waveform which is a change in pressure between the pressure determined in f) iii) and the pressure determined in f) v), divided by the change in time between the time determined in f) ii) and the time determined in f) iv).
 24. The system of claim 23, wherein the software further enables the computer to normalize the V waveform negative slope value to the heart beat frequency of the individual to obtain a normalized negative slope number (NNSN).
 25. The system of claim 24, wherein the computer normalizes the V waveform negative slope to the heart be frequency of the individual by using the formula (ΔP/ΔT)(SfH)/(MfH), wherein ΔP is change in pressure between the pressure determined in f) iii) of claim 21 and the pressure determined in f) v) of claim 21, wherein ΔT is the change in time between the time determined in f) ii) of claim 21 and the time determined in f) iv) of claim 21, wherein MfH is a measured heart rate in the person, and wherein SfH is a selected heart beat frequency conversion factor.
 26. The system of claim 25, wherein SfH is selected to convert MfH to one beat per second.
 27. The system of claim 23, wherein the catheter comprises a second balloon suitable for positioning adjacent to the aortic arch and recording changes in aortic arch pressure to obtain an aortic arch pressure waveform.
 28. The system of claim 27, wherein the software further enables the computer to determine a time of occurrence of a dicrotic notch in the aortic arch pressure waveform.
 29. The system of claim 23, wherein the peak of the V waveform coincides with opening of a mitral valve.
 30. The system of claim 23, wherein the sensor is a second balloon suitable for positioning adjacent to the aortic arch and recording changes in aortic arch pressure to obtain an aortic arch pressure waveform.
 31. The system of claim 23, wherein the sensor is a phonocardiograph machine.
 32. The system of claim 23, wherein the device for measuring the heart rate of the person is a sphygmomanometer. 